Method and apparatus for feeding and compacting finely divided particulate material

ABSTRACT

A method of feeding and compacting finely divided particulate material, which utilizes a rotating screw feeder for advancing the material along a sleeve passage provided by a stationary foraminous sleeve mounted closely about the screw feeder. The method includes the steps of advancing the particulate material axially along the sleeve with the interstitial air between the particles in the sleeve at an internal sleeve pressure. Suction pressure relatively lower than the internal sleeve pressure is applied to the exterior of the sleeve to withdraw air from between the particles of the material to effect compaction of the material. At predetermined times gas pressure relatively higher than the internal sleeve pressure is applied to the exterior of the sleeve to back-flush material from openings in the sleeve to prevent clogging thereof. An apparatus for feeding and compacting finely divided particulate material, which includes a housing having fixedly mounted therein a tubular sleeve. The sleeve and housing define at least one closed hollow chamber extending about the sleeve with a plurality of perforations in the sleeve placing the interior thereof in fluid communication with the interior of the chamber. An axially extending screw feeder concentrically and rotatably mounted in the sleeve is adapted to advance material axially along the sleeve, with the interstitial air present between the particles of material in the sleeve at an internal sleeve pressure. Suction means in fluid communication with the chamber applies suction pressure relatively lower than the internal sleeve pressure to withdraw air from between the particles of material to affect compaction thereof. Gas pressure means in fluid communication with the chamber provides gas at a relatively higher pressure than the internal sleeve pressure at predetermined times to backflush particulate material from the perforations, to prevent clogging thereof.

United States Patent Inventor ABSTRACT: A method of feeding andcompacting finely divided particulate material, which utilizes arotating screw feeder for advancing the material along a sleeve passageprovided by a stationary foraminous sleeve mounted closely about thescrew feeder. The method includes the steps of ad vancing theparticulate material axially along the sleeve with the interstitial airbetween the particles in the sleeve at an internal sleeve pressure.Suction pressure relatively lower than the internal sleeve pressure isapplied to the exterior of the sleeve to withdraw air from between theparticles of the material to effect compaction of the material. Atpredetermined times gas pressure relatively higher than the internalsleeve pressure is applied to the exterior of the sleeve to backflushmaterial from openings in the sleeve to prevent clogging thereof.

An apparatus for feeding and compacting finely divided particulatematerial, which includes a housing having fixedly mounted therein atubular sleeve. The sleeve and housing define at least one closed hollowchamber extending about the sleeve with a plurality of perforations inthe sleeve placing the interior thereof in fluid communication with theinterior of the chamber. An axially extending screw feederconcentrically and rotatably mounted in the sleeve is adapted to advancematerial axially along the sleeve, with the interstitial air presentbetween the particles of material in the sleeve at an internal sleevepressure. Suction means in fluid communication with the chamber appliessuction pressure relatively lower than the internal sleeve pressure towithdraw air from between the particles of material to affect compactionthereof. Gas pressure means in fluid communication with the chamberprovides gas at a relatively higher pressure than the internal sleevepressure at predetermined times to backflush particulate material fromthe perforations, to prevent clogging thereof.

[72] Clarence E. Carter Danville, III. [2]] Appl. No. 718,123 [22] FiledApr. 2, 1968 [4S] Patented May 25, I971 [73] Assignee Carter EngineeringCompany Danville, Del.

[54] METHOD AND APPARATUS FOR FEEDING AND COMPACTING FINELY DIVIDEDPARTICULATE MATERIAL 7 Claims, 5 Drawing Figs.

[52] US. Cl 222/1, 222/189, 222/413 [51] Int. Cl B67d 5/88 [50] Field ofSearch 222/189, 193, 413, 1, 152.53; 141/7, 8, 59, 67, 286; 55/302, 452

[56] References Cited UNITED STATES PATENTS 2,170,469 8/1939 Carter141/7 2,142,990 1/1939 Belcher. 151/286X 2,985,201 5/1961 Baker 14l/59X3,269,611 7/1966 Komarek 222/413X 3,333,679 8/1967 Zimmerman et al....222/413X Primary Examiner-Robert B. Reeves Assistant Examiner-H. S. LaneAttorney-Bums, Doane, Swecker and Mathis I i i J 4.

u s l| l4 METHOD AND APPARATUS FOR FEEDING AND COMPACTING FINELY DIVIDEDPARTICULATE MATERIAL BACKGROUND OF THE INVENTION This invention relatesto a method and apparatus for feeding and compacting finely dividedparticulate material, such as for example fluffy powders and the like.

In handling finely divided particulate material such as for fluffypowders, it is sometimes necessary to reduce the bulk of the powderwhile it is being fed from one location to another. This may beparticularly necessary in packaging operations, for a number of reasons.For example, once packaged in containers, such powders have a tendencyto settle out during storage and transit with the result that thecontainers may appear partially empty and underpacked on opening.Additionally, it may be necessary to provide for compaction in order toreduce required container dimensions to an acceptable size.

Accordingly, various systems have heretofore been proposed forsimultaneously feeding and compacting materials of this type. One priorsystem for example utilizes a screw feeder having a helical flight ofdecreasing pitch so that as the material is advanced into the moreclosely spaced region of the flight, it is mechanically compressed.Unfortunately, such mechanical compression of fluffy powders may oftenbe undesirable due to the tendency of such particles in the powder tobind together under the influence of the mechanical compression. Thismay result in providing a product of uneven consistency, andadditionally may lead to bridging of the material.

Another approach, intended to obviate the disadvantages of mechanicalcompression, has been to permit the particulate material to falldownwardly through the interior of a foraminous sleeve while applyingvacuum to the exterior of the sleeve to cause air to be removed from theparticulate material, thus compacting it. Systems of this type, however,suffer from the disadvantage that the foraminous sleeve may rapidlybecome clogged with particles of the material. Such clogging has atleast two significant disadvantages. Firstly, it may reduce the abilityof the perforations, en masse, to transmit suction to the interior ofthe sleeve, thus reducing the rate at which air is removed from thepowder. Secondly, the distribution of the clogging may often be unevenlydistributed about the sleeve with the result that suction is unevenlyapplied to the material during feeding. This may lead to undesirablevariations in the consistency of the final compacted material.

Another problem associated with such foraminous sleeve type devices isthat the vacuum applied may tend to hold some of the particulatematerial in static relation against the interior of the sleeve, thusreducing the overall rate at which material may be be fed.

SUMMARY OF INVENTION It is therefore a general object of the inventionto provide a method and apparatus for feeding and compacting finelydivided particulate materials, which obviates or minimizes problems ofthe type previously noted.

It is a particular object of the invention to provide a method andapparatus for feeding and compacting finely divided particulate materialin which the material continues to be compacted uniformly duringprotracted operation, to provide a product of particularly evenconsistency.

It is a further object of the invention to provide an apparatus forfeeding and compacting finely divided particulate material utilizing aforaminous sleeve in which problems of clogging of the sleeve withparticles of the material are effectively reduced.

A method of feeding and compacting finely divided particulate material,intended to accomplish at least some of the foregoing objects utilizes arotating screw feeder for advancing the material through a stationaryforaminous sleeve mounted closely about the screw feeder. The methodincludes the steps of advancing the particulate material axially throughthe sleeve with the interstitial air between particles in the materialin the sleeve being at an internal sleeve pressure. A suction pressurerelatively lower than the internal sleeve pressure is applied to theexterior of the sleeve to withdraw air from between the particles of thematerial to effect compaction of the material. Gas at a gas pressurerelatively higher than the internal sleeve pressure is applied to theexterior of the sleeve at predetermined times to back-flush particulatematerial from the perforations in the sleeve to prevent cloggingthereof.

In a further method aspect of the invention the step of applying gaspressure includes the further steps of providing noncommunicating,closed 'hollow chambers about different peripherally spaced areas of thesleeve. The gas pressure is then applied to each of the chambers in turnat predetermined times during which the other of the chambers hassuction pressure applied thereto. In this manner the pressuredifferential across the perforations in the sleeve is increased toassist the back-flushing action.

An apparatus for feeding and compacting finely divided particulatematerial, according to a preferred embodiment of the invention includesa housing having fixedly mounted therein a tubular sleeve. The sleeveand adjacent interior portions of the housing define at least one closedhollow chamber extending about the sleeve. The sleeve further includes aplurality of perforations placing the chamber in communication with theinterior of the sleeve. An axially extending screw feeder concentricallyand rotatably mounted in the sleeve feeds particulate material axiallyalong the sleeve with the interstitial air present between the particlesin the material in the sleeve, being at an internal sleeve pressure.Suction means connected with the housing is placed in fluidcommunication with the chamber to apply a suction pressure relativelylower than the internal sleeve pressure to withdraw air from the particulate material, thus effecting compaction of it. Gas pressure meansconnected with the housing, is placed in fluid communication with thechamber at predetermined times for supplying gas at a gas pressurerelatively higher than the internal sleeve pressure to the perforations.In this manner, the particulate material is periodically back-flushedfrom the perforations in the sleeve to prevent clogging.

In a further aspect of the invention, partition means are providedextending between the sleeve and the housing, to divide the chamber intoat least two axially extending, noncommunicating subchambers extendingperipherally about different portions of the sleeve. The suction meansfurther includes first and second suction means each communicatingdifferent ones of the subchambers. Similarly, the gas pressure meansincludes first and second gas pressure means each communicatingdifferent ones of the subchambers. In operation each of the gas pressuremeans is connected in turn to its associated pressure subchamber at atime during which the other of the subchambers is concurrently connectedto its associated suction means. In this manner an increased pressuredifferential to assist in back-flushing gas through the perforations inthe sleeve is created.

THE DRAWINGS An apparatus for feeding and compacting finely dividedparticulate materials according to a preferred embodiment of theinvention, is illustrated in the accompanying drawings in which,

FIG. 1 is a side view of an apparatus according to a preferredembodiment of the invention;

FIG. 2 is a cross-sectional, end view of a portion of the apparatusshown in FIG. 1 TAKEN ALONG THE LINES 2-2 therein;

FIG. 3 is a cross-sectional view of a portion of the apparatus shown inFIG. 2, but on an enlarged scale;

FIG. 4 is a cross-sectional top view of the portion of the apparatusshown in FIG. 2 taken along the lines 4-4 therein; and

FIG. is a side view of a lower end check valve forming a part of itsapparatus shown in FIG. I.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawings, an apparatusfor feeding and compacting finely divided particulate material accordingto a preferred embodiment of the invention is there shown.

The apparatus includes a housing, generally designated 2 connected tothe lower end of a conventional hopper 3 containing a mass of theparticulate material. Positioned within the housing 2' is an axiallyextending foraminous, circular sleeve 4 (FIG. 2), having an axiallyextending internal sleeve passage communicating at its upper end withthe interior of the hopper 3. The tube 2 and the housing 4 define anenclosed hollow chamber 6 extending about the sleeve. Extending throughthe sleeve 4 is a concentric circular shaft 8 supported in fixedrelation to the sleeve for rotation relative thereto, by suitableconventional bearing structure (not shown) connected with the housing. Ascrew flight l0, fixedly secured to the shaft 8, extends between theshaft and the interior of the sleeve and advances the particulatematerial downwardly axially through the sleeve passage from the hopper 3during rotation of the shaft 8.

Suction at a pressure lower than that within the sleeve is applied tothe chamber 6 (as will be described) to withdraw the interstitial airfrom between the particles of material as it is being fed through thetube, to cause the material to become compacted. To prevent the vacuumfrom causing some of the particulate material to adhere in staticcondition to the interior of the sleeve, the conveyor flight I0 isprovided with a downwardly projecting thin sheet metal lip 11 secured tothe peripheral edge of the flight, which shears any adhered powder fromthe interior of the sleeve. At predetermined times, air is supplied tothe chamber 6 at a pressure higher than thatin the interior of thesleeve to cause air to pass in a reverse direction through the sleeveperforations to back-flush particulate material therefrom to preventclogging.

In more detail, the housing 2 includes an axially extending, verticallydisposed, tubular metal body 12 of circular cross section. Ari inwardlyextending, horizontally disposed annular bottom plate 14 is fixedlysecured to the lower end of the tube 12 by welding, although otherconventional methods may be used. The bottom plate 114 includes anupwardly facing, peripherally extending rectangular notch 15 (FIG. 3)which receives and supports the lower end of the sleeve 4 and locates itin spaced concentric relation to the interior of the tubular body 12. Atits upper end, the tubular body 12 is fixedly secured to a radiallyoutwardly extending, annular top plate 16 (FIG. 2) spaced radially fromthe sleeve 41 and having a flat horizontal upper surface.

An annular top member 18 is fixedly secured to the flat upper surfaceofthe top plate 16 by suitable elongate threaded connectors 17. The topmember 18 extends axially upwardly and is provided with a peripherallyextending, internal chamber 20 facing toward the sleeve 4 andcommunicating with the previouslymentioned annular space 6 between thetubular body I2 and the sleeve. The top member 18 also includes aperipherally extending flange 2ll projecting radially inwardly adjacentthe upper end of the top member and provided with a downwardly facingperipherally extending, rectangular notch 22 for receiving andsupporting the top end of the sleeve 4 and locating it concentrically ofthe housing.

In order to prevent leakage of air a seal between the sleeve 4 and thehousing 2 at the top and bottom ends of the sleeve is provided by theuse of suitable sealing materials between the notches 22 and 15 and thesleeve.

The previously mentioned conveyor flight 10 is formed of sheet metalextending in helicoidal fashion about the shaft 8 and is rotated byconventional means (not shown) in such a direction as to advancematerial downwardly through the sleeve. At its upper end the sleeve 4and the conveyor communicate with the hopper 3 containing a supply ofthe particulate material. The material in the supply contains a certainamount of interstitial air, between the particles in the material.Usually this interstitial air will be at substantially atmosphericpressure although use of a supply functioning at pressures above orbelow atmospheric pressure is possible. As the material is fed throughthe sleeve the interstitial air is at an internal sleeve pressuresubstantially equal to that prevailing in the supply, i.e., usuallyatmospheric pressure.

During passage of the material by the screw conveyor through the sleeve,the previously mentioned suction pressure is applied to the exterior ofthe sleeve. This suction pressure is less than the internal sleevepressure to cause a large portion of the interstitial air to be suckedout of the conveyed material, thus compacting it. For example, utilizinga supply under atmospheric pressure, the suction pressure may typicallybe of the order of 25 inches of mercury vacuum.

As suction is applied to the sleeve 4, however, some of the particulatematerial may tend to become held statically by the vacuum to' theinterior surface of the sleeve 4, thus resisting motion axially downthrough the sleeve. To provide for removal of this static powder, thepreviously mentioned thin sheet metal lip 11 secured to the conveyorflight along the outer peripheral edge thereof extending axiallydownstream, is provided. The lip efficiently shears the powder from theinterior surface of the sleeve to ensure that all the powder is fed downthrough the sleeve at a uniform rate.

In addition, the lip insures that the interior of the sleeve is blankedoff from vacuum for a relatively substantial area adjacent the shearingedge of the lip so that the powder is only loosely attached at the timeof shearing. This prevents the effect of suction extending about theedge of the screw flight alone which might otherwise tend to hold someparticles in position even during scraping.

To render the sleeve 4 foraminous, a plurality of radial perforations 26spaced regularly along and about the sleeve are provided. For reasons ofease of manufacture the perforations 26 are usually likely to be greaterthan the average particle size of the powders transported. In order,therefore, to prevent particles from being sucked through into thechamber 6, a mesh screen 27 having smaller mesh openings than the sizeof the particles in the transported material, is disposed in contiguousoverlapping relation to the exterior surface of the sleeve extendingbetween the lower plate 14 and the top flange 21. The mesh screen 27prevents the passage of particles through the perforations 26 into thechamber 6 in order to prevent the chamber from becoming filled up withpowder.

Referring to FIG. 4, the previously mentioned annular chamber 6 togetherwith the chamber 20 in the top member 18 is divided by two diametricallyopposed partitions 30 and 32 into two noncommunicating, axiallyextending subchambers 6a and 6b extending about opposite peripheralhalves of the exterior of the sleeve. The partitions 30 and 32 arefixedly secured to the housing 2 and the sleeve 4, extending axiallybetween the sleeve and housing.

Suitable sealing materials are applied at the junction between the innerends of the partitions 30 and 32 and adjacent portions of the meshscreen 27 overlying the exterior of the sleeve to prevent leakage of airbetween the partitions and the exterior of the sleeve.

To provide for the application of suction to the interior of thesubchamber 6a, a conduit 34, threadedly engaged with a radiallyextending opening 36 in the top member 18, is provided. The conduit 34at one end communicates through the opening 36 with the interior of thesubchamber 6a and at its remote end communicates with a suitable sourceof suction such as a vacuum pump P through a selectively controlledfirst suction valve 38 interposed in the conduit 3d. When the valve 38is selected to be open, vacuum is applied to the interior of the chamber60 to suck air outwardly through the sleeve, thus compacting adjacentparticulate material fed through the sleeve by the screw conveyor.

A similar conduit 40 and second suction valve 42 for applying suction tothe subchamber 6b are also provided.

After a certain period of feeding, some of the perforations 26 arelikely to have become clogged with particles of the material being fed.It is necessary to remove this material in order that vacuum may stillbe applied evenly to the interior of the sleeve.

For this purpose another conduit 50 threadedly engaged with acorresponding opening 52 extending radially through the top member 18,is provided. The conduit 50 communicates at its inner end with thesubchamber 6a through the opening 52 and its remote end communicateswith atmosphere through a selectively openable first gas valve 54interposed in the conduit 50.

A similar conduit 56 and second gas valve 58 are provided for placingthe subchamber 6b in fluid communication with atmosphere.

The valves 38, 42, S4 and 58 enable the pressure conditions within thehousing 2 to be regulated in the following manner. For a majority of thetime the gas valves 54 and 58 are 'closed, with the suction valves 38and 42 concurrently open to apply suction pressure to the subchambers 6aand 6b so that suction is applied about the entire peripheral area ofthe sleeve to remove air from the particulate material being fed.

At a predetermined time, the first gas valve 54 is opened and the firstsuction valve 38 closed, so that atmospheric pressure is admitted to thesubchamber 6a. At the same time, suction is still being applied to thesubchamber 6b communicating with the interior of the sleeve with theresult that the internal sleeve pressure is reduced below atmosphericpressure. Thus, the atmospheric air admitted through the valve 54constitutes a source of gas at relatively higher pressure than theinternal sleeve pressure. This pressure differential (with the exteriorof the sleeve at atmospheric pressure and the interior stillcommunicating with a vacuum source) causes any accumulated particulatematerials in the perforations 26 to be back-flushed out of theperforations into the interior of the sleeve to unclog them. After anadequate period of time to allow for unclogging to be completed thefirst gas valve 54 is closed and the first suction valve 38 reopened toonce again apply suction to the subchamber 6a.

At another predetermined time, the second suction valve 42 is closed andthe second gas valve 58 opened, to place the subchamber 6b in fluidcommunication with atmosphere at a time when the subchamber 611 stillhas vacuum applied thereto. At this time, the perforations 26 in thatportion of the sleeve communicating with the subchamber 6b, will be backflushed in a manner similar to that just described.

This process may be repeated on a regular basis to keep the sleeve 4operating in a substantially unclogged condition during continuedfeeding of the particulate material, utilizing suitable timingmechanism.

To prevent air from being drawn in from atmosphere through the bottomend of the sleeve 4 which would diminish the effect of the vacuum beingapplied to the material in the sleeve, a flexible lower end check valve60 (FIGS. 1 and 5) is secured to the lower end of the housing 2. Thevalve 60 comprises a flexible sleeve with the sleeve walls of the valve60 converging inwardly and downwardly into flat abutting relation in onevertical plane passing diametrically of the sleeve. The lower edge ofthe sleeve is provided with a diagonally, downwardly extending loweredge 62.

The sleeve walls of the valve 60 are distended apart to permit downwardand outward passage of the particulate material but are urged togetherby atmospheric pressure to prevent passage of air into the lower end ofthe sleeve.

Although the invention has been described with reference to utilizingatmospheric pressure for back-flushing purposes, it will be appreciatedthat alternatively the conduits 50 and 56 could be connected to positivepressure sources, such as gas pumps or cylinders of stored gas,operating at pressures substantially in excess of atmospheric pressure.Also each suction valve may be adapted for venting to atmosphereconcurrently with the adjacent gas pressure valve.

In a combination of back-flushing actions, atmospheric pressure mayinitially be utilized for a predetermined time to provide a first stageof back-flushing in which clogged material is pulled from theperforations by the suction still applied to the other subchamber. Thenthe back-flushing pressure may be increased by a gas pump in a secondstage of back-flushing to, in effect, push any residual clogged materialfrom the perforations.

As another alternative possibility, it would be possible to dispenseentirely with the partitions dividing the annular space into twosubchambers, and utilize a single chamber extending entirely about thesleeve with periodic applications of positive pressure thereto toback-flush the accumulated particulate material present in theperforations.

SUMMARY OF ADVANTAGES It will be appreciated that in following themethod and apparatus of the present invention for feeding and compactingfinely divided particulate material, certain significant advantages areprovided.

In particular, the invention provides a method and apparatus for feedingand compacting finely divided particulate material utilizing aforaminous screen, which provides for continued operation without lossof efiiciency due to clogging of the screen.

Another significant advantage is provided by the downwardly extendinglip provided about the edge of the conveyor flight which shears off anymaterial held by vacuum against the interior of the sleeve, to provideimproved feeding characteristics.

Other advantages are provided by theprovision of the noncommunicatingsubchambers and the system of valves connecting the various suction andair pressure conduits, functioning in such a manner as to cause thesuction applied to one of the subchambers to assist the action ofatmospheric pressure applied to the other of the subchambers to providea back-flushing pressure differential across the sleeve.

Furthermore, the manner in which the sleeve is simply mountedconcentrically in an annular outlet housing obviates the disadvantagesof certain earlier structures, exemplified by US. Pat. No. 3,269,61 l(Komarek) which required the basic hopper structure to be modified bythe provision of complicated recessed portions in the main hopper wallitself.

Although the invention has been described with reference to onepreferred embodiment, it will be appreciated that numerous additions,modifications, substitutions, deletions, and other changes notspecifically disclosed may be made which will fall within the purview ofthe appended claims.

lclaim:

l. A method of continuously feeding and compacting finely dividedparticulate material utilizing a rotating screw feeder for advancing thematerial through a sleeve passage provided by a stationary foraminoussleeve mounted closely about the screw feeder, the method comprising thesteps of:

mechanically advancing the particulate material along the sleeve passagewith the interstitial air between particles of the material in thesleeve being at an internal sleeve pressure,

applying, from a suction pressure system, a suction pressure relativelylower than the internal sleeve pressure along the exterior of the sleeveto withdraw at least a portion of the interstitial air from between theparticles of the material through the sleeve to effect compaction of thematerial,

providing noncommunicating closed hollow chambers axially extending thelength of the sleeve about different peripherally spaced areas of thesleeve;

applying, while continuing to mechanically advance the material, a gaspressure relatively higher than the internal sleeve pressure along thelateral surface of each of the chambers in turn at predetermined timesduring which the other of the chambers has suction pressure appliedthereto to cause a pressure differential across the perforations toback-flush particulate material from the perfora tions in the sleeve toprevent clogging thereof; and simultaneously preventing gas pressurefrom entering the end of the sleeve passage and the suction pressuresystem.

2. A method of feeding and compacting finely divided particulatematerial as defined in claim 1 and further comprising the steps of:

utilizing an axially advancing screw blade having an axially extendinglip flush with the interior surface of the sleeve scraping the adheredmaterial from the interior surface all along the sleeve,

simultaneously spirally blanking off portions of the interior of thesleevefrom the vacuum in the area embraced by the axially extendingblade lip to diminish the suction forces causing the particulatematerial to adhere to the interior of the sleeve during scrapingthereof, and

opening the interior of the sleeve to vacuum in the area following thearea embraced by the advancing blade.

3. An apparatus for feeding and compacting finely divided particulatematerial having interstitial air between the particles, the apparatuscomprising:

a housing,

a tubular sleeve fixedly mounted in said housing, said sleeve andadjacent interior portions of said housing defining, at least one closedhollow chamber extending about said sleeve;

said sleeve further including,

a plurality of perforations placing said chamber in fluid communicationwith the interior of said sleeve;

an axially extending screw feeder concentrically and rotatably mountedin said sleeve, said feeder upon rotation thereof adapted to feed theparticulate material axially along said sleeve with the interstitial airbeing at an internal sleeve pressure;

partition means within said chamber extending between and fixedlysecured to said housing and sleeve, said partition means dividing saidchamber into at least two axially extending, noncommunicatingsubchambers extending peripherally about different portions of said ssleeve;

suction means connected with said housing for selectively applyingsuction pressure relatively lower than the internal sleeve pressurethrough said perforations to the interior of said sleeve to withdrawalong the lateral surface of the sleeve at least a portion of theinterstitial air from the particulate material to effect compactionthereof during feeding including first suction means communicating onlywith one of said subchambers and,

second suction means communicating only with the other of saidsubchambers;

gas pressure means connected with said housing for supplying gas at arelatively higher pressure than the internal sleeve pressure to saidperforations along the lateral surface of said sleeve at predeterminedtimes to back-flush particulate material from said perforations toprevent clogging thereof, including first gas pressure meanscommunicating only with said one of said subchambers; and second gaspressure means communicating only with said other of said subchambers.4. An apparatus as defined in claim 3 wherein said screw feederincludes,

an axially extending shaft concentrically positioned within and spacedfrom said sleeve, an axially extending screw flight secured to saidshaft extending generally helically therealong, said flight includmg, aperipheral edge closely adjacent interior portions of said sleeve, a lipfixedly secured to said screw flight extending continuousl alon said eriheral ed e said li extendin axially dowiistrean fro said edge aid said11% being in contact with adjacent interior portions of said sleeve.

5. An apparatus as defined in claim 3 further including,

a tubular sleeve check valve connected with said sleeve adjacent anoutlet end of said passage for restrictively permitting outward passageof particulate material through the sleeve to maintain a back pressureon the material and preventing ingress of air into said outlet passage.

6. An apparatus as defined in claim 3 further including,

first and second suction valves connected with said first and secondmeans respectively, each of said suction valves upon opening thereofplacing the associated one of said first and second suction means influid communication with the associated one of said subchambers; and

first and second gas valves connected with said first and second gaspressure means respectively, each of said gas valves upon openingthereof placing the associated one of said first and second gas pressuremeans in fluid communication with the associated one of saidsubchambers,

said first gas valve being opened concurrently with closing of saidfirst suction valve at predetermined times during which said second gasvalve is closed and said second suction valve is open, said second gasvalve being opened concurrently with closing of said second suctionvalve at other predetermined times during which said first gas valve isclosed and said first suction valve is open.

7. An apparatus as defined in claim 3 further including,

a layer of perforate mesh of smaller mesh size than the size of theparticles, said layer of mesh contiguously overlying said sleeve on asurface hereof facing inwardly of said chamber.

1. A method of continuously feeding and compacting finely dividedparticulate material utilizing a rotating screw feeder for advancing thematerial through a sleeve passage provided by a stationary foraminoussleeve mounted closely about the screw feeder, the method comprising thesteps of: mechanically advancing the particulate material along thesleeve passage with the interstitial air between particles of thematerial in the sleeve being at an internal sleeve pressure, applying,from a suction pressure system, a suction pressure relatively lower thanthe internal sleeve pressure along the exterior of the sleeve towithdraw at least a portion of the interstitial air from between theparticles of the material through the sleeve to effect compaction of thematerial, providing noncommunicating closed hollow chambers axiallyextending the length of the sleeve about different peripherally spacedareas of the sleeve; applying, while continuing to mechanically advancethe material, a gas pressure relatively higher than the internal sleevepressure along the lateral surface of each of the chambers in turn atpredetermined times during which the other of the chambers has suctionpressure applied thereto to cause a pressure differential across theperforations to back-flush particulate material from the perforations inthe sleeve to prevent clogging thereof; and simultaneously preventinggas pressure from entering the end of the sleeve passage and the suctionpressure system.
 2. A method of feeding and compacting finely dividedparticulate material as defined in claim 1 and further comprising thesteps of: utilizing an axially advancing screw blade having an axiallyextending lip flush with the interior surface of the sleeve scraping theadhered material from the interior surface all along the sleeve,simultaneously spirally blanking off portions of the interior of thesleeve from the vacuum in the area embraced by the axially extendingblade lip to diminish the suction forces causing the particulatematerial to adhere to the interior of the sleeve during scrapingthereof, and opening the interior of the sleeve to vacuum in the areafollowing the area embraced by the advancing blade.
 3. An apparatus forfeeding and compacting finely divided particulate material havinginterstitial air between the particles, the apparatus comprising: ahousing, a tubular sleeve fixedly mounted in said housing, said sleeveand adjacent interior portions of said housing defining, at least oneclosed hollow chamber extending about said sleeve; said sleeve furtherincluding, a plurality of perforations placing said chamber in fluidcommunication with the interior of said sleeve; an axially extendingscrew feeder concentrically and rotatably mounted in said sleeve, saidfeeder upon rotation thereof adapted to feed the particulate materialaxially along said sleeve with the interstitial air being at an internalsleeve pressure; partition means within said chamber extending betweenand fixedly secured to said housing and sleeve, said partition meansdividing said chamber into at least two axially extending,noncommunicating subchambers extending peripherally about differentportions of said s sleeve; suction means connected with said housing forselectively applying suction pressure relatively lower than the internalsleeve pressure through said perforations to the interior of said sleeveto withdraw along the lateral surface of the sleeve at least a portionof the interstitial air from the particulate material to effectcompaction thereof during feeding including first suction meanscommunicating only with one of said subchambers and, second suctionmeans communicating only with the other of said subchambers; gaspressure means connected with said housing for supplying gas at arelatively higher pressure than the internal sleeve pressure to saidperforations along the lateral surface of said sleeve at predeterminedtimes to back-flush particulate material from said perforations toprevent clogging thereof, including first gas pressure meanscommunicating only with said one of said subchambers; and second gaspressure means communicating only with said other of said subchambers.4. An apparatus as defined in claim 3 wherein said screw feederincludes, an axially extending shaft concentrically positioned withinand spaced from said sleeve, an axially extending screw flight securedto said shaft extending generally helically therealong, said flightincluding, a peripheral edge closely adjacent interior portions of saidsleeve, a lip fixedly secured to said screw flight extendingcontinuously along said peripheral edge, said lip extending axiallydownstream from said edge and said lip being in contact with adjacentinterior portions of said sleeve.
 5. An apparatus as defined in claim 3further including, a tubular sleeve check valve connected with saidsleeve adjacent an outlet end of said passage for restrictivelypermitting outward passage of particulate material through the sleeve tomaintain a back pressure on the material and preventing ingress of airinto said outlet passage.
 6. An apparatus as defined in claim 3 furtherincluding, first and second suction valves connected with said first andsecond means respectively, each of said suction valves upon openingthereof placing the associated one of said first and second suctionmeans in fluid communication with the associated one of saidsubchambers; and first and second gas valves connected with said firstand second gas pressure means respectively, each of said gas valves uponopening thereof placing the associated one of said first and second gaspressure means in fluid communication with the associated one of saidsubchambers, said first gas valve being opened concurrently with closingof said first suction valve at predetermined times during which saidsecond gas valve is closed and said second suction valve is open, saidsecond gas valve being opened concurrently with closing of said secondsuction valve at other predetermined times during which said first gasvalve is closed and said first suction valve is open.
 7. An apparatus asdefined in claim 3 further including, a laYer of perforate mesh ofsmaller mesh size than the size of the particles, said layer of meshcontiguously overlying said sleeve on a surface hereof facing inwardlyof said chamber.